Performance of ultraviolet exposed epoxy powder coatings functionalized with silica by hot mixing

The effect of hydrophilic nanosilica additions on the (1–3% by wt.) mechanical performance of epoxy powder coatings after UV exposure was investigated in this study. The epoxy coatings were prepared by mixing a commercial epoxy powder with nanoparticles in a hot mixer, an alternative method that is simpler than extrusion. Powders were electrostatically applied on carbon steel and cured to obtain coatings. The epoxy-based coatings were exposed to a xenon lamp with an irradiance of 550 W·m−2 for 500 h. Chemical structure of coatings was characterized before and after xenon exposure, using an attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Glass transition temperature (Tg) was measured with differential scanning calorimetry (DSC). Mechanical and wear tests were performed in order to study the difference among the coatings without and with silica nanoparticles after UV exposure. Surface of the coatings was analyzed with scanning electron microscopy (SEM), as well as the wear tracks to assess the wear mechanism. Finally, aesthetic properties (gloss and color) were also evaluated. The results confirm that the use of SiO2 nanoparticles in amounts up to 2% allows less chemical and physical degradation of the surfaces and better wear resistance than the plain epoxy coatings after xenon exposure was found for 1% coating.